Which of the following informs the body that it's time to sleep?

Question

Quizplus · Accepted Answer

The pineal gland is an endocrine system gland that releases melatonin, which helps the body by telling it when it is time to sleep.
Pituitary glands release growth hormones. 
The thyroid is an endocrine system gland responsible for controlling an individual's metabolism by producing the hormones triiodothyronine and thyroxine. The thyroid is found in the front of an individual's neck.
The adrenal glands secrete hormones such as cortisol, which helps regulate your metabolism, and adrenaline, which helps your body respond to stress.

Which of the Following Informs the Body That It's Time